Soil organic carbon stocks in saline and sodic landscapes

Abstract

Increasing salinity (high levels of water-soluble salts) and sodicity (high levels of exchangeable sodium) are serious land degradation issues worldwide. In Australia, salinity and sodicity affect a large proportion of the landscape and often coincide with agricultural land. Despite the areal extent of salt-affected soils, both worldwide and in Australia, few data exist on soil organic carbon (SOC) stocks in these areas. For this study, the level of SOC was determined in scalded (bare areas without vegetation), scalded-eroded, vegetated, and revegetated (i.e. sown pasture) soil profiles from 2 sites in the Southern Tablelands region of New South Wales, Australia. SOC concentration was significantly higher in the profiles that were vegetated with native pasture (1.96-2.71% in the 0-0.05 m layer) or revegetated with sown pasture (2.35% in the 0-0.05 m layer), and lower in those profiles that were scalded (1.52% in the 0-0.05 m layer) or scalded-eroded (0.16-0.30% in the 0-0.05 m layer). These lower SOC levels are reflected throughout the profiles of the scalded and scalded-eroded soils. The soil carbon stocks to 0.30 m are also much lower in the scalded and scalded-eroded soils that have been affected by salinity and sodicity. The profiles that were vegetated with native pasture had carbon stocks to 0.30 m of 35.2-53.5 t/ha, while the sown pasture had 42.1 t/ha. This compares with the scalded profiles with 19.8 t/ha and the scalded-eroded profiles with 7.7-11.4 t/ha to 0.30 m. The presence of vegetation ameliorates several soil properties and results in the differences in SOC and other soil properties between scalded and vegetated profiles at the surface and at depth.